The invention relates to an injection system for an internal combustion engine, according to the preamble of claim 1, and to a method for regulating and/or bleeding an injection system for an internal combustion engine, according to the preamble of claim 9.
Such injection systems for internal combustion engines conventionally have a pre-feed pump which feeds the fuel to be injected out of a fuel tank via a fuel line and transfers it to a high-pressure pump which generates the injection pressure necessary for injecting the fuel into the combustion spaces of the internal combustion engine. In the case of a common-rail injection system, the high-pressure pump is connected on the outlet side to a high-pressure accumulator, from which the injectors assigned to the individual combustion spaces of the internal combustion engine procure the fuel to be injected.
The known injection systems also make it possible to scavenge the high-pressure pump with the fuel to be injected, with the result that a lubrication and cooling of the high-pressure pump are brought about. For this purpose, a feed branches off, between the pre-feed pump and the high-pressure pump, from the fuel line connecting the pre-feed pump to the high-pressure pump and issuing on the outlet side into the casing of the high-pressure pump. Via the feed, part of the fuel conveyed by the pre-feed pump is branched off and used for scavenging the high-pressure pump. The fuel used for scavenging purposes is subsequently returned to the fuel tank via a fuel return line.
As a result of the scavenging of the high-pressure pump by the fuel stream branched off from the feed stream, however, when the internal combustion engine is started the pressure build-up on the intake side of the high-pressure pump is delayed or even prevented, so that the internal combustion engine starts only with a retard or not at all. A regulating valve is therefore arranged in the feed branching off between the pre-feed pump and the high-pressure pump, said regulating valve releasing the scavenging stream in the feed only when the fuel pressure necessary for operating the high-pressure pump is reached on the intake side of the high-pressure pump.
In the known injection systems, the pre-feed pump and the high-pressure pump are driven via a mechanical connection by the internal combustion engine of the common-rail system, so that the rotational speed of the pre-feed and the high-pressure pump is proportional to the engine rotational speed. Since the rotational speed of the high-pressure pump is a function of the engine rotational speed, at low engine rotational speeds, which occur, for example, during starting, the high-pressure pump conveys only a relatively low volume flow into the high-pressure accumulator. For a rapid start of the engine, however, a rapid pressure build-up in the high-pressure accumulator is necessary. It is therefore necessary for the entire injection system to be constantly filled completely with fuel and contain as far as possible no air bubbles or gas bubbles. However, by the fuel tank being emptied, due to maintenance work on the system or as a result of leaks, air may infiltrate into the system. In order to prevent a delayed pressure build-up during the starting operation due to the included air in the system, therefore, bleeding devices are provided.
Normally, for bleeding the injection system in this way, individual bleeding valves or throttles are installed, in addition to the regulating valve for the scavenging stream, in the feed in the low-pressure region between the pre-feed pump and the high-pressure pump. What is to be achieved thereby is that the air can be discharged via the bleeding valves or throttles and cannot pass into the displacement spaces of the high-pressure pump. When a throttle is used, on the one hand, it is necessary, for a rapid escape of air, that the throttle has a relatively large throughflow cross section. On the other hand, the selected size of the throughflow cross section of the throttle must be sufficiently small, so that as little fuel as possible can escape through the throttle. A satisfactory dimensioning of the throttle in terms of the size of the throughflow cross section is therefore difficult to achieve. By contrast, when nonreturn valves are used as a bleeding device, it is always necessary to build-up a specific pressure in the fuel line, in order to open the nonreturn valve and thus bleed the injection system. In this case, however, at low starting rotational speeds of the engine, problems arise with regard to the build-up of a corresponding pressure which is sufficient for opening the nonreturn valve. The bleeding of the injection system is therefore not always ensured.
Furthermore, it is known to install a bleeding valve, in which a closing body is guided in a guide of the bleeding valve. Between the guide and the closing body is provided a capillary gap, via which the air included in the system is discharged during the bleeding operation. After bleeding, the fuel flows into the capillary gap. In this case, due to the high flow resistance of the fuel in the capillary gap, the closing body is taken up, so that the bleeding valve is closed by the closing body. Where a wetted capillary gap is concerned, however, there is the problem that the closing body is moved into its sealing position even during bleeding and the air can no longer escape completely through the capillary gap. Sufficient bleeding of the injection system is consequently difficult to achieve.
The object on which the invention is based is therefore to provide an injection system which can be bled simply and reliably, a rapid pressure build-up in the high-pressure accumulator being ensured at the same time, and a method for regulating and/or bleeding such an injection system.
This object can be achieved by an injection system for an internal combustion engine, comprising a pre-feed pump, a high-pressure pump, a high-pressure accumulator and at least one injector, which are connected to one another via a fuel line, in order to convey fuel out of a fuel tank via the pre-feed pump and the high-pressure pump into the high-pressure accumulator and to inject said fuel out of the high-pressure accumulator via the injector into a combustion chamber of the internal combustion engine, a feed for the high-pressure pump, said feed being connected to the fuel line between the pre-feed pump and the high-pressure pump, in order to supply fuel for lubrication and cooling to the high-pressure pump, and a valve device connected to the feed, which regulates the fuel stream for lubricating and cooling the high-pressure pump and/or bleeds the injection system, wherein the valve device comprises at least one movably arranged actuator and a first and a second throttle device, the actuator being set as a function of a pressure of the fuel stream between the pre-feed pump and the high-pressure pump, in such a way that a first connection through the first throttle device to the high-pressure pump is released or the feed to the high-pressure pump is interrupted or a second connection through the second throttle device to the high-pressure pump is released.
The object can also be achieved by an injection system for an internal combustion engine, with a pre-feed pump, a high-pressure pump, and a high-pressure accumulator which are connected to one another via a fuel line, in order to convey fuel out of a fuel tank via the pre-feed pump and the high-pressure pump into the high-pressure accumulator, a feed for the high-pressure pump, said feed being connected to the fuel line between the pre-feed pump and the high-pressure pump, in order to supply fuel for lubrication and cooling to the high-pressure pump and to bleed the injection system, and a valve device connected to the feed, which regulates the fuel stream for lubricating and cooling the high-pressure pump and which bleeds the injection system, and wherein the valve device comprises at least one movably arranged actuator and a first and a second throttle device, the actuator being set as a function of a pressure of the fuel stream between the pre-feed pump and the high-pressure pump, in such a way that a first connection through the first throttle device to the high-pressure pump is released or the feed to the high-pressure pump is interrupted or a second connection through the second throttle device to the high-pressure pump is released.
The first and the second throttle device may have different throughflow cross sections. The first and/or the second throttle device can be designed to be integrated in the actuator. The actuator may have at least one passage duct. The actuator can be designed as a throughflow-cross section actuator or pressure actuator. The valve device may comprise at least one directional valve and/or at least one pressure limiting valve. The throttle devices, the directional valve and/or the pressure limiting valve can be assembled in the valve device. The actuator can be set in such a way that the first connection through the second throttle device and the first throttle device is released.
Consequently, the injection system according to the invention has a pre-feed pump which supplies the high-pressure pump additionally with fuel for lubrication and cooling by means of a feed branching off from the fuel line to the high-pressure pump. In this case, the feed has arranged in it a valve device which, on the one hand, regulates the fuel stream for the lubrication and cooling of the high-pressure pump and, on the other hand, bleeds the injection system. Thus, before or during an operation to start the engine, the air included in the injection system can be discharged from the injection system via the valve device. Furthermore, the valve device ensures, preferably in interaction with an admission-pressure regulating valve and a high-pressure regulating valve, that the feed is interrupted, after bleeding, during the operation of starting the internal combustion engine. As a result of the interruption, it is possible that a pressure builds up in the fuel line to the high-pressure pump during the starting operation and that the high-pressure pump is filled completely with fuel. Moreover, in the event of a further pressure rise downstream of the pre-feed pump, there is provision for the valve device to release a scavenging path to the high-pressure pump. For this purpose, the valve device comprises at least one integrated actuator arranged movably in the valve device and also a first and a second throttle device.
As a function of a pressure of the fuel in the feed upstream of the valve device, the actuator in each case assumes a position in which either a first connection through the first throttle device to the high-pressure pump is released or the feed to the high-pressure pump is interrupted or a second connection through the second throttle device to the high-pressure pump is released. The combination according to the invention of the two throttle devices with the actuator in the valve device affords the great advantage that the fuel stream supplied from the pre-feed pump to the high-pressure pump is both regulated and at the same time bled via the valve device. The valve device according to the invention reacts automatically to the respective operating states of the engine via the pressure prevailing in each case in the fuel line downstream of the pre-feed pump. This ensures the bleeding of the system, a rapid pressure build-up in the high-pressure accumulator and therefore also an easy restarting of injection systems which contain included air.
It is preferred that the first and the second throttle device have different throughflow cross sections. It is thereby possible to adapt the throughflow cross sections of the individual throttles to a respective application. In this case, the first throttle device, which is preferably provided for bleeding the injection system, has, for example, a relatively small throughflow cross section, so that as little fuel as possible can escape. By contrast, the throughflow cross section of the second throttle device, via which the fuel stream for scavenging the high-pressure pump is conducted, is dimensioned sufficiently large for a reliable delivery of fuel for scavenging the high-pressure pump to be ensured. The throttle devices are thus in each case to be suitably dimensioned individually for the respective application.
For a compact form of construction of the valve device, advantages are afforded when the first and/or the second throttle device are designed to be integrated in the actuator of the valve device. As a result, even under confined conditions of space, the respective throttle device can be positioned at a desired point in the valve device.
For connecting a valve inlet to a valve outlet of the valve device, it has been shown to be advantageous for the actuator to have at least one passage duct, through which the fuel stream flowing through the valve device is conducted. The passage duct may be designed in a structurally simple way as a bore through the actuator.
It is further preferred for the actuator to be provided as a throughflow-cross section actuator or pressure actuator. As a result, in the event of a change in the pressure in the fuel line, a diversion of the throughflow paths of the fuel through the valve device can be achieved quickly and reliably. Thus, a double function of the valve device as a bleeding valve and a scavenging valve can be implemented in a simple way. Advantages are afforded, in this respect, when the valve device comprises at least one throughflow-cross section regulating valve or pressure regulating valve. For example, by providing at least one directional valve and/or at least one pressure limiting valve in the valve device, an adjustment of the throughflow path in the valve device can be achieved particularly simply and easily.
Furthermore, for a compact form of construction of the valve device, advantages are afforded, when the throttle devices, the at least one directional valve and/or the at least one pressure limiting valve are assembled in the valve device. The valves are in this case integrated in a structural element designed as a combination valve. As a result, even when the installation space in the high-pressure pump is restricted, the valve device can be connected reliably to the feed.
The object can also be achieved by a method for regulating and/or bleeding an injection system for an internal combustion engine, comprising a pre-feed pump, a high-pressure pump, a high-pressure accumulator and at least one injector, which are connected to one another via a fuel line, the method comprising the steps:
conveying fuel out of a fuel tank via the pre-feed pump and the high-pressure pump into the high-pressure accumulator,
injecting the fuel out of the high-pressure accumulator via the injector into a combustion chamber of the internal combustion engine,
branching off fuel for lubricating and cooling the high-pressure pump via a feed from the fuel line between the pre-feed pump and the high-pressure pump, and
regulating the fuel stream in the feed and/or bleeding the injection system by means of a valve device, and
moving at least one movably arranged actuator of the valve device essentially between three different positions in the valve device as a function of a pressure of the fuel stream between the pre-feed pump and the high-pressure pump.
In an initial position of the actuator, a first connection through a first throttle device to the high-pressure pump can be released and, with an increasing dynamic pressure of the fuel flowing through the valve device, the actuator can be moved out of its initial position into a second position, in which the first connection to the high-pressure pump is essentially interrupted, and subsequently into a third position, in which a second connection through a second throttle device to the high-pressure pump is released. In the initial position of the actuator, the first connection may run both through the second throttle device and through the first throttle device to the high-pressure pump. The fuel flow through the first connection can be lower than the fuel flow through the second connection. The fuel flow through the first connection can be lower than the fuel flow through the second connection.
As can be seen from the foregoing, according to the method, fuel for lubricating and cooling the high-pressure pump is branched off via a feed from the fuel line between the pre-feed pump and the high-pressure pump, the fuel stream being regulated and/or the injection system bled by means of the valve device in the feed. In this case, both the regulation of the fuel stream in the feed and the bleeding of the injection system are achieved by means of at least one actuator which is arranged movably in the valve device and which is adjusted essentially between three different positions in the valve device as a function of a pressure of the fuel stream in the feed. The pressure acting on the actuator in the valve device affords the great advantage that the valve device reacts automatically to the respective operating states and to the resulting pressures in the fuel line. This considerably simplifies the control and regulation of the fuel stream in the injection system. Furthermore, the movement of the actuator in the valve device also ensures the bleeding of the fuel system, so that a delayed pressure build-up due to air included in the injection system is effectively prevented.
According to an advantageous embodiment of the method according to the invention for regulating and bleeding the injection system, in a position of rest of the actuator a first connection through a first throttle device to the high-pressure pump is released. In the position of rest of the actuator, the bleeding of the injection system takes place, the air being discharged out of the low-pressure region to the high-pressure pump via the first throttle device. After bleeding, the actuator is moved, with an increasing dynamic pressure of the fuel stream flowing through the valve device, out of its position of rest into a second position, in which the connection to the high-pressure pump is essentially closed. In the second position, the feed is interrupted, that is to say essentially no scavenging stream flows to the high-pressure pump, so that the entire bled fuel stream is conveyed from the pre-feed pump to the high-pressure pump via the fuel line and a rapid pressure build-up in the high-pressure pump is ensured. Since the entire fuel stream is available for the pressure build-up, a delayed starting of the internal combustion engine is prevented. In the event of a further pressure rise, the actuator is moved into a third position, in which a second connection through a second throttle device to the high-pressure pump is released. In the third position, the fuel volume flow branched off from the fuel line via the feed flows to the high-pressure pump, in order to cool and lubricate the latter.
In a further embodiment, there flows through the first throttle device, in the position of rest of the actuator, a fuel stream which amounts to between ⅓ and ⅔ of the fuel quantity conveyed overall by the pre-feed pump. For example, during starting, the pre-feed pump conveys about 150 ml, about 5-10 ml flowing through a scavenging duct for bleeding. In the third position, several 100 ml can flow through the scavenging duct and consequently through the second throttle device for cooling through the high-pressure pump. In this case, at the changeover from the position of rest to the second position, the dynamic pressure preferably amounts to 0.2-0.4 bar. The changeover between the second position and the third position of the actuator is preferably between 1.5 and 2 bar. In this case, the inlet valve or inlet valves of the high-pressure pump open at about 0.7 bar. In embodiments with a higher opening pressure of the inlet valve, the changeover points between the position of rest and the second position or the second position and the third position of the actuator are displaced correspondingly.